Extraction process



May 29, 1945- M. souDERs, JR 2,377,049

EXTRACTION PROCESS Filed Nov. 5, 1942 2 Sheets-Sheet 1 buianzs +Acz1onzf II8 l cous Andorre Concen'ra'fzd) Solvzn Edurn Line Figi May 29, 1945.M, SOUDERS, JR 2,377,049

EXTRACTION PROCESS Filed Nov. 3, 1942 2 Sheets-Sheet 2 queoueAczioneConccnfmred) Fig. n

Patented May 29, 1945 Ex'mAo'rIoN raocEss Mott Souders, Jr., Piedmont,Calif., assigner to Shell Development Company, San Francisco, Calif., acorporation of Delaware Appuootiop November s, 1942, serial No. 464,403

(ci. iss- 115) 6 Claims.

This invention relates to the separation of hydrocarbon mixtures ofnarrow boiling range which are diflicultly separable by ordinaryfractionation. More particularly, the invention relates to theseparation lof narrow boiling hydrocarbon mixtures containing two vormore components of diii'erent degrees of saturation.v

The invention is especially valuable in connection with the separationof olefins of four car bon atoms from normal butane and as so appliedconstitutes an improvement on the process described in copendingapplication S'erial No. 332,366, which issued as Patent No. 2,371,908 onMarch 20, 1945.

In the process of the above-identified copending application, mixturesof olefins and parailins or mono-olefins and dioleflns are separated bycontacting them with an aqueous organic solvent, the organic constituentof which may be acetone, for example, to selectively dissolve the moreunsaturated component which isL obtained as a highly purified materialupon subsequent regeneration of the solvent solution as by distillation.The process is conveniently executed by passing the mixture to beseparated in countercurrent relation to the aqueous solvent in a 'columnprovided with suitable contact and/or acetone to the treatment ofmixtures of olefins of four carbon atoms as normal butylenes andisobutylene with normal butane has given rise to considerable operatingdifficulty because of loss of acetone with the overhead vapors. This isbelieved to result, partially at least, from the formation of anazeotrope of normal butane and acetone, since the diiculty is notcorrected by the employment of additional rectifying plates between thesolvent inlet port and the top of the column. By means of suchrectifying or knockdown plates it is sometimes possible in distillationor extraction processes of the type involved to prevent any substantialloss of solventwith the overhead, but this expedient has been foundvalueless as to mixtures containing normal butane.

A further operating diflioulty, experienced not only during thetreatment of mixtures containing normal butane but also during thetreatment of mixtures free of this hydrocarbon, results from theaccumulation in the aqueous organic solvent of hydrocarbons of a highermolecular weight than the hydrocarbons inthe mixture being separated.Mixtures of the type subjected to the treatment according to the processof application, Serial No. 332,366, are obtained, for example, by thepyrolysis of petroleum or petroleum fractions. Although by ordinaryfractionation it is relatively easy to obtain cuts or fractions from thepyrolyzed product which predominate in hydrocarbons of the same numberof carbon atoms, it is practically impossible to achieve absolutelyclean separation. Thus, a C4 hydrocarbon cut will invariably becontaminated with at least minor amounts of amylenes, pentanes,pentadienes, etc. Upon subsequent continuous extraction of the C4fraction these higher molecular Weight hydrocarbons tend to build up inthe solvent with a consequent adverse eii'ect upon its emciency.

A principal object of the present invention is to provide an improvedprocess for effecting the recovery of acetone from the overhead producedwhen a mixture comprising one or more oleflns together with one or moreparailins, particularly a mixture comprising one or more oleflns of fourcarbon atoms together with normal butane, is extracted with an aqueousacetone solvent. Another object is to effect continuous recovery of theacetone content of the overhead in a manner providing for its immediaterecirculation. Still another object is to provide an improved processfor separating olefins from parafllns by means of an aqueous acetonesolvent wherein the lean or regenerated solvent produced incident to therecovery of the extracted olefln is continuously or intermittently freedof undesirable hydrocarbon accumulate. A still further object is toprovide an improved process which is generally applicable to theseparation of narrow boiling hydrocarbon mixtures containing componentsof different degrees of saturation as mixtures of mono-olens anddiolens, mono-oleflns and/or diolens and parailins, etc.

According to the present invention, as carried out using an aqueoussolution of acetone as the selective solvent, the acetone-containingoverhead vapors from the extraction column are condensed with theformation of two liquid phases. The upper or hydrocarbon phase is reeturned to the extraction column as reflux, while the lower phase, whichis relatively rioher in acetone, is introduced into ascrubbing zone,which may conveniently be a second column or tower, wherein it isscrubbed with water. The acetone solution obtained through the scrubbingoperation is separated from the undissolved component or components andconveyed to a distillation unit which is operated under such conditionsas to produce an aqueous acetone solution of a strength equivalent tothat of the solution being employed in the extraction tower. I'heaqueous acetone solution so produced may be returned' to the extractiontower either directly or from intermediate storage.

In the execution of the invention using aqueous acetone as the selectivesolvent, water washing is also employed to eiect the removal oftheundesirable hydrocarbon accumulate from the regenerated solvent producedupon distillation of the olen solution from the extraction column.According to one embodiment of the invention the water washing of theregenerated or lean solvent is carried out in the same scrubbing zoneinto which the acetone rich phase of the extraction column overhead isintroduced.

The invention will be more clearly understood from the followingdetailed description and the accompanying flow diagrams illustrative ofmethods of applying it. Figure I represents a system adapted especiallyto the separation of mixtures of normal butane and other hydrocarbons offour carbon atoms having a lesser degree of saturation by means of anaqueous acetone solvent. Figure II represents a modification of thissystem. The drawings indicate only the essential and/or desirableapparatus elements and their relation to each other, minor elements suchas pumps, compressors, valves, and the like being in the main omitted.Proper lplacement of these auxiliaries will at once be evident to thoseskilled in the art to which the invention pertains.

With reference to Figure I, the numeral IIl denotes an extraction columnprovided with the heat source shown as a closed heating coil II throughwhich may be circulated a heating medium, such as steam, hot oil, andthe like. The mixture to be separated, which will be considered asconsisting of alpha and beta butylenes, normal butane and isobutane, isintroduced into column I via line I2 at approximately the pointindicated. As the gaseous mixture ascends into the column III, it is metby a descending stream of an aqueous acetone solution, having an acetoneconcentration of from about 75 to about 90 percent, introduced into thecolumn III'via line lI3 at a. point below the point of introduction ofthe feed mixture. The olenic content of the feed mixture is selectivelydissolved by the aqueous acetone solvent which has a preferentialaflinity therefor. Any paraflln hydrocarbon, e. g. butanes, dissolved bythe solvent is substantially completely removed therefrom in the lowerportion of the column, which is maintained at a relatively highertemperature than the rest of the column by means of the heating coil II.The solution of olenns in the aqueous acetone solvent is conveyed fromcolumn IIJ through line I4 to stripping column I5, which is providedwith a heat source I6 also indicated as a closed heating coil. Column Iis operated at a temperature sufiicient to remove the dissolved olenswhich are recovered as overhead. The stripped or lean solvent isWithdrawn from column I5 through line I'I which communicates withsolvent feed line I3 as shown.

The top or overhead product from extraction column I0 consisting of thebutanes present in the original mixture plus acetone is conveyed throughan overhead vapor line I8 to a condenser and phase separator I9. Twoliquid layers arey formed in condenser I9. Each layer contains bothacetone and paraflin hydrocarbon but the lower layer is relativelyricher in acetone than the upper. Controlled quantities of the liquid inthe upper layer are preferably returned to the extraction column as reuxvia reflux line 2U, while the lliquid in the lower layer is conveyedthrough linev 2I to a scrubbing tower 22 wherein it is scrubbed withwater admitted through line 23. This serves to' separate substantiallyall of the butanes which have only negligible solubility in water. Thedilute aqueous acetone solution resulting from the scrubbing operationis withdrawn through line 25 to a concentrating column 26. It should benoted that if desired all of the liquid which accumulates incondenser-separator I9 may be conveyed to tower 22, but best resultshave been found to follow by operating with reflux as described.

Column 25 shown as equipped with a heat source 2l, an overhead vaporline 28, and a condenser 29 is operated to produce an overhead fractionconsisting of acetone and water, which fraction has an acetoneconcentration substantially equivalent to the aqueous acetone solventbeing employed in extraction column ID and a bottom fraction consistingof water. The condensed overhead is withdrawn from condenser 29 throughline 30 which communicates with lines Il and I3 as shown, while thewater fraction may be recycled as in the drawing to the scrubbing tower.

As previously herein indicated, it is highly desirable that the solventrecycled to the extraction column I0 be substantially completely free ofhydrocarbon material. For the purpose of avoiding the accumulation inthe solvent of hydrocarbon material not removed by the strippingoperation in column I5, a line 3l, which may be called the regeneratedsolvent clean-up line, is provided. This line terminates near the bottomof scrubbing column 22.

The rate of take-off or the amount of regenerated solvent withdrawn fromline II through line 3I and thence to column 22 varies within widelimits, being determined primarily by the purity of the khydrocarbonfraction beingseparated. This in turn depends upon the source of thefraction, or in the case of cuts derived from pyrolyzed petroleumfractions upon the efliciency of the available prefractionationequipment. In operating upon a butylene-butane fraction separated from apyrolyzed petroleum fraction with ordinary refinery fractionatingequipment, it has been found that the solvent may be maintained in nearoptimum condition by directing from about 1,4m to about 1/10 of theregenerated solvent into line 3I. The hydrocarbon material separatedfrom the regenerated solvent withdrawn from line I'I via line 3| isrecovered from column 22 as overhead along with the butanes separatedfrom the extraction column overhead.

It should be mentioned that, if desired, all of the regenerated solventfrom the stripping column may be water-washed before its re-introductioninto the extraction column. The waterwashing of either all or a part ofthe regenerated solvent may be carried out in tower 22 as shown, that isin the same tower in which the overhead from the extraction column isscrubbed or in a second scrubbing tower.

Still further modifications of the invention will immediately suggestthemselves. For example, it may be advantageous where it is desired tocontinuously water-wash all or a large portion of the regeneratedsolvent prior to its re-use in the extraction column to employ both thecolumn in which the overhead from the extraction column is scrubbed anda second column, the regenerated solvent to be washed being proportionedeither equally or otherwise between the two columns. Also, theemployment of a second or, for that matter, a third or a still greaternumber of scrubbng columns or towers may be coupled with water scrubbingof all or a part of the stripping column overhead, that is the overheadfrom column I which, under certain circumstances, may contain sulcientacetone to justify such op.. eration. Thus the system used mayapproximate the modification disclosed in Figure II wherein likenumerals refer to like parts in Figure I.

In Figure II the overhead from stripping column |5 is conveyed via line32 to a second scrubbing tower or column 33. Water is supplied to column33 through line 35. A line 33 extends from stripping column exit line I1to column 33, terminating near the bottom of the column, while a branchline 31 extends from line 36 to the bottom portion of the scrubbingtower 22. Under this arrangement, and assuming of course theincorporation of suitable control valves in the system, any desiredamount of the regenerated solvent from the stripping column may beconveyed to either of the two scrubbing towers. The top fractionproduced by column 33 consists of the olens dissolved by the aqueousacetone solvent in the extraction column plus the hydrocarbon accumulateseparated from the regenerated s01- vent by the washing operation. Thedilute aqueous acetone solution produced as bottom product may beconcentrated to the desired strength for use in the extraction columneither in a second concentrating column 38, as shown, to which column itis conveyed by line 39, or, if desired, in column 26. In the latterevent column 28 is necessarily of greater capacity than where only thedilute solution from column 22 is concentrated therein.

When operating with a single concentrating column, the bottom productsof each of the scrubbers may be combined and introduced into theconcentrating column at a single point, while the water fractionconstituting the bottom product of the concentrating column may be splitin proper proportion between the two scrubbing towers.

If the system comprises the use of a second concentrating column, asshown in the drawings, that is column 38, the concentrated overhead isintroduced after condensation into the solvent return line just as inthe case of the concentrated overhead from column 26, while the waterbottom fraction is recycled to scrubbing tower 33 via line 35.

It is to be understood that execution of the invention may not entailthe water scrubbing of the extraction column overhead but only waterscrubbing of the overhead from the stripping column I5. In this casecolumns 22 and 26 may or may not form part of the system.

The improved process of the present invention is advantageous in the twomajor respects that the solvent employed in .the extraction column iscompletely recovered for re-use and is at the same time maintained in astate of highest operating eiilciency. Although especially applicable,

as stated, to the separation of vnarrow boiling hydrocarbon fractionscomprising normal butane, as mixtures of butadiene and/or butylenes withnormal butane, it may be applied with equal success to the treatment ofother narrow boiling hydrocarbon mixtures as mixtures of ethylene andethane, propylene and propane, butadiene and butylenes, amylenes andpentadienes, amylenes and/or pentadienes and pentanes, etc.

The invention is not limited to extraction or distillation operationsinvolving the use of aqueous organic solvents but may be put into effectwhere the extraction is carried out with an anhydrous solvent having therequired degree of selectivity. Nor is it necessary for the solvent tohave a greater aillnity for the more unsaturated of the components to beseparated as the process is ap.- plicable where non-polar solvents, suchas ether, trichlorethylene, carbon tetrachloride, etc., are used. Innon-polar solvents, such as those specically named, parafllns arerelatively more soluble than olens and mono-olens are relatively moresoluble than dioleilns; hence, the more saturated component is extractedrather than the more unsaturated.

Among the many solvents, which like aqueous or anhydrous acetone have a.preferential solvent power for the more unsaturated components asbetween components of different degrees of saturation, may be mentioned:furfural, ethylene chlorhydrin, epichlorhydrin, nitriles, as acetoandpropionitrilesy dichlorethyl ether, dimethyl glycerol ether, isocrotylchloride, acid anhydrides, as the anhydrides of acetic and propionicacids, etc.

When operating with an anhydrous solvent, the solvent concentratingcolumn or columns are of course operated to produce an anhydrous productfor recycle. It should also be mentioned that it may be advantageous insome cases to use a liquid other than water as the scrubbing agent toproduce the dilute substantially hydrocarbon-free solution or solutionsof the solvent. Like water, the liquid used should have relativelylittle solvent power for hydrocarbons. For example, ethylene glycol,glycerol, trimethylene glycol, ethylene diamine, ethanolamine, etc. maybe used in lieu of water when operating with anhydrous acetone.

I claim as my invention:

l. In a process which comprises contacting a gaseous mixture containinga butylene and normalv butane with an aqueous acetone solvent to producea solution of the butylene in the aqueous acetone solvent, whichsolution after separation from the residual mixture is subsequentlytreated to recover the butylene therefrom and to produce a regeneratedacetone solvent, the improvement which comprises subjecting the residualmixture to condensation conditions under which two liquid phases areformed, the lower of said phases being relatively richer in acetone thanthe upper, passing the liquid in the lower phase and at least a part ofthe regenerated solvent produced upon recovery of the butylene into ascrubbing zone, scrubbing the said liquid and the regenerated solventpassed into said zone with water to separate hydrocarbon materialtherefrom and to produce a dilute aqueous solution of acetone,concentrating the dilute aqueous solution of acetone to an acetoneconcentration substantially equivalent to the acetone concentration ofthe aqueous acetone solvent employed to produce the solution of thebutylene, and employing the concentrated solution to extract additionalquantities o! the butylene.

2. In a process which comprises contacting a mixture containing anoleiin and a parain of similar boiling temperatures and having the samenumber of carbon atoms per molecule, with an aqueous acetone solvent toproduce a solution of the olen in the aqueous acetone solution, whichsolution after separation from the residual mixture is subsequentlytreated to recover the olefin therefrom and to produce a regeneratedacetone solvent, the improvement which comprises subjecting the residualmixture to condensation conditions under which two liquid phases areformed, the lower of said phases being relatively richer in acetone thanthe upper, passing the liquid in the lower phase and at least a part ofthe regenerated solvent produced upon recovery of the olefin into ascrubbing zone, scrubbing the said liquid and the regenerated solventpassed into said zone with water to separate hydrocarbon materialtherefrom and to produce a dilute aqueous solution of acetone,concentrating the dilute aqueous solution of acetone to an acetoneconcentration substantially equivalent to the acetone concentration ofthe aqueous acetone solvent employed to produce the solution of theolen, and employing the concentrated solution to extract additionalquantities of the oleiin.

3. In a process for the separation of a narrow boiling hydrocarbonmixture containing a component of a different degree of saturation buthaving the same number of carbon atoms as a component from which it isto be separated, which process comprises contacting said hydrocarbonmixture with a selective solvent to produce a solution of the saidcomponent in the solvent, which solution after separation from theresidual mixture is subsequently treated to recover said hydrocarboncomponent therefrom and to produce a. regenerated solvent, theimprovement which comprises subjecting the residual mixture tocondensation conditions under which two liquid phases are formed, thelower of said phases being relatively richer in selective solvent thanthe upper, passing the liquid in the lower phase and at least a part ofthe regenerated solvent produced upon recovery of the aforementionedhydrocarbon component into a scrubbing zone, scrubbing the said liquidand the regenerated solvent passed into said zone with a liquid havingrelatively little solvent power for hydrocarbons to produce a dilutedsubstantially hydrocarbon-free solution of the selective solvent,concentrating said diluted solution to substantially the strength of thesolvent employed to produce the solution of the said hydrocarboncomponent, and employing the concentrated solvent to dissolve additionalquantities of the said hydrocarbon component.

4. In a process for the separation of a narrow boiling hydrocarbonmixturecontaining a diolen and a more saturated hydrocarbon of similarboiling temperature and having the same number of carbon atoms permolecule, with an aqueous acetone solvent to produce a solution of thedioleiin in the aqueous acetone solution, which solution afterseparation from the residual mixture is subsequently treated to recoverthe diolen therefrom and to produce a regenerated acetone solvent, theimprovement which comprises subjecting the residual mixture tocondensation conditions under which two liquid phases are formed, thelower of said phases being relatively richer in acetone than the upper,passing the-liquid in the lower phase and at least a part oftheregenerated solvent produced upon recovery of the diolen into ascrubbing zone, scrubbing the said liquid and the regenerated solventpassed into said zone with water to separate hydrocarbon materialtherefrom and to produce a dilute aqueous solution of acetone,concentrating the dilute aqueous solution of acetone to an acetonevconcentration substantially equivalent to that of the aqueous acetonesolvent employed to produce the solution of the diolen, and employingthe concentrated solution to extract additional quantities of thediolefln.

5. In a process which comprises contacting a gaseous mixture containinga butadiene and a butylene with an aqueous acetone solvent to produce asolution of the butadiene in the aqueous acetone solvent, which solutionafter separation from the ,residual mixture is subsequently treated torecover the butadiene therefrom and to produce a regenerated acetonesolvent, the improvement which comprises subjecting the residual mixtureto condensation conditions under which `two liquid phases are formed,the lower of said phases being relatively richer in acetone than theupper, passing the liquid in the lower phase and at least a part of theregenerated solvent produced upon recovery of the butadiene into ascrubbing zone, scrubbing the said liquid and the regenerated solventpassed into said zone with water to separate hydrocarbon materialtherefrom and to produce a dilute aqueous solution of acetone,concentrating the dilute aqueous solution of acetone to an acetoneconcentration substantially equivalent to that of the aqueous acetonesolvent employed to produce the solution of the butadiene, and employingthe concentrated solution to extract additional quantities of thebutadiene.

6. In a process which comprises contacting a gaseous mixture containinga pentadiene and an amylene with an aqueous acetone solvent to produce asolution of the pentadiene in the aqueous acetone solvent, whichsolution after separation from the residual mixture is subsequentlytreated to recover the pentadiene therefrom and to produce a regeneratedacetone solvent, the improvement which comprises subjecting the residualmixture to condensation conditions under which two liquid phases areformed, the lower of said phases being relatively richer in acetone thanthe upper, passing the liquid in the lower phase and at least a part ofthe regenerated solvent produced upon recovery of the pentadiene into ascrubbing zone, scrubbing the said liquid and the regenerated solventpassed into said zone with water to separate hydrocarbon materialtherefrom and to produce a dilute aqueous solution of acetone,concentrating the dilute aqueous solution of acetone to an acetoneconcentration substantially equivalent to that of the aqueous acetonesolvent employed to produce the solution oi the pentadiene, andemploying the concentrated solution to extract additional quantities ofthe pentadiene.

MOTT SOUDERS, Jn.

